Ergot is a type of fungus that primarily infects cereal grains, particularly rye. It produces dark, elongated structures called sclerotia, which can replace the grain kernels. These sclerotia contain various alkaloids that can be toxic to humans and animals if ingested. Historically, ergot has been associated with a condition known as ergotism, which can cause severe symptoms like hallucinations, convulsions, and gangrene. Despite its dangers, some compounds derived from ergot have been used in medicine, such as ergotamine, which is used to treat migraines.